This invention relates generally to a highly flexible catheter having a balloon at its distal tip. The form of the catheter is such that it may be used in various percutaneous transluminal angioplasty (PTA) procedures but is sufficiently flexible in its construction that it may be used for other diagnostic and treatment indications in regions of the body having significantly more tortuous vasculature.
For instance, in PTCA procedures, a guiding catheter typically having a preshaped distal tip is introduced into the vasculature of a patient. The catheter is advanced from the entry point, up into the aorta and, once at that site, is twisted or torqued from the proximal end of the catheter so to turn the preshaped distal tip of the guiding catheter in to the ostium of a desired coronary artery. A balloon-bearing or "dilatation" catheter is then advanced through the lumen of a guiding catheter and is progressed out the guiding catheter's distal tip until the balloon on the distal extremity of the dilatation catheter extends cross the region to be dilated. The balloon is then expanded, typically to a predetermined size dictated by the design of the balloon, via the use of radio-opaque liquid at relatively high pressures. Upon completion of the procedure, the balloon is then deflated so that the dilatation catheter can be removed and blood flow resumed through the thus-treated artery.
In other procedures, a balloon-bearing catheter typically of a somewhat smaller diameter than a catheter used in PTA or PCTA might be used. In a universal sense, the procedure might be considered to be similar in that a larger or guiding catheter is initially placed so that its distal end is near the body site to be treated or diagnosed. The balloon-catheter, perhaps with the guidewire through an existing central lumen, would then be extended from the distal end of the guiding catheter to the site. the balloon is expanded and once the procedure is complete, the balloon is deflated and removed from the body. In some instances, the balloon might be of a compliant nature rather than the fixed diameter configuration found in a typical PTA balloon.
The advent of interventional radiology as a viable alternative in neurological regions of the body have produced demands on catheterization equipment not faced by demands placed on PTCA devices. The need for significantly smaller diameter devices, devices having a variable flexibility, ability to resist kinking (particularly in those regions where the differences in flexibility may be acute) is notable.
One way to produce strong catheter shafts for a balloon catheter is via the use of braids in those shafts. For instance, U.S. Pat. No. 5,338,295, to Cornelius et al. describes a dilatation balloon catheter having a shaft formed of a tubular stainless steel braid. The proximal outer tube section is encased in a polyimide material. The distal outer tube section which forms the balloon is made of a polymeric material such as polyethylene. The braid in this instance extends only partially down the proximal portion of the catheter. It does not extend as far as the balloon nor does it extend through the balloon.
Another similar device is shown in U.S. Pat. No. 5,451,209, to Ainsworth et al. Ainsworth et al. describes a composite tubular element useful in intravascular catheters. In particular it is shown as an element, variously of a fixed wire dilatation catheter and in a guiding or angiographic catheter. The structure of the device is made by braiding strands from a mixture of a polymeric matrix materials (such as fibers or powders) having a relatively low melting point and a high strength reinforcing fiber having a relatively high melting point. The fibers are woven into a tubular element; the resulting braided tubular element is heated to melt the low melting point matrix material so as to flow around the reinforcing fibers to form a matrix. Thermoplastic jackets or coatings are then extruded or otherwise applied to the exterior of the thus-produced braided tubular element. There is no suggestion in the patent to either produce a shaft which has variable stiffness proximally nor to use only a metallic braid from the proximal end of a over the wire catheter to a position distal of the balloon.
U.S. Pat. No. 5,429,597 to DeMello, teaches a balloon catheter which is said to be kink resistant. In general, it appears to be made up of an outer polymeric covering over a "cross-wound multifilar (CWMF)" coil and a non-fixed, removable core wire. The CWMF coil is a pair of helical coils which are wound in opposite directions to provide for torque transmission during use. There appears to be no suggestion of weaving the CWMF into a braid. There is no suggestion of extending the CWMF through the length of the balloon interior.
The PCT application to Pray et al. (WO 93/20881) assigned to Scimed Medical Systems suggests a dilatation catheter having a shaft with a proximal section which is a composite of polymeric material and a stainless steel braid tube. The distal section of the catheter is formed of a flexible polymeric tube. In one embodiment of the described device, the braid weave of the proximal section of the shaft has a varying pick count, increasing in the distal direction, thereby providing for increased flexibility in the distal direction. However, this document does not suggest the use of a braided tube extending distally of the balloon. Furthermore, there is no suggestion of the use of an elastomeric or rubbery balloon on the device.
Published UK Patent Application G.B. 2,233,562A, by Hannam et al., shows a balloon catheter having a flexible, hollow inner shaft and an outer braided shaft with a balloon inflated by fluid introduced between the inner and outer shafts. The inner shaft is fixed relative to the outer shaft at both ends. When the balloon is inflated, the outer shaft shortens. The excess length of the inner shaft is accommodated via the inner shaft bending into a coil-like form. The braid is said typically to be of a fabric of a polyester floss. It is said to extend the entire length of the outer shaft but with a varying pick rate apparently in the neighborhood of the balloon. The balloon is made of the material of the loose braided layer and a flexible, elastic polyurethane. There is no suggestion of using the braided material as an overall stiffener in the balloon catheter device. There is no suggestion of placing the braid on the interior of the balloon.
None of the published documents teaches the inventive balloon catheter.